Work done in moving a charge

1. The problem statement, all variables and given/known data
What is the work done in moving a 0.2 µC point charge from corner a to b of a square abcd, when a 10 µC charge exists at the center of the square?

2. Relevant equations
Work or ΔU=q*V
V=kq/r

3. The attempt at a solution
V=kq/r
V=(9.0x10^9)(0.2x10^-6)/r

This is where I get stuck because there is no r given. We can assume that all the sides of the square are equal and the distance to the 10 µC charge is half of that. But I feel like an actual value should be given.1. The problem statement, all variables and given/known data

Staff: Mentor

That's not correct. Electric force is conservative, which means work done depends on the difference between potential in the starting and ending point. So the more correct way of expressing it would be ΔU=q*ΔV. Now think what ΔV is.

Edit: ap123 answered while I was composing the answer, but we are aiming at exactly the same thing.